1. Field of the Invention
The present invention generally relates to a drive method for a piezoelectric actuator. More specifically, the present invention relates to a drive method for a piezoelectric actuator, a drive apparatus for a piezoelectric actuator, an electronic device, a control program for the drive device of a piezoelectric actuator, and a recording medium.
2. Background Information
Piezoelectric elements have an excellent conversion ratio of electrical energy to mechanical energy, and also have excellent responsiveness. Various piezoelectric actuators that utilize the piezoelectric effects of piezoelectric elements have therefore been recently under development. These piezoelectric actuators are applied to a field that includes various electronic devices, such as piezoelectric buzzers, inkjet heads in printers, ultrasonic motors, electronic timepieces, and portable devices.
However, in piezoelectric actuators, the resonance frequency fluctuates due to the influence of the surrounding temperature, the load, and the like. Therefore, the frequency of the drive signal capable of driving the piezoelectric actuator also fluctuates according to the surrounding temperature, the load, and the like.
Examined Patent Application (Kokoku) No. 5-16272 (hereinafter referred to as Prior Art 1) discloses a system in which the frequency of the drive signal is swept or varied within a wide range that includes the frequency range of the fluctuating drive signal, and the motor is reliably driven. Prior Art 1 is hereby incorporated by reference. Specifically, in Prior Art 1, the sweep voltage of a triangular wave or a sawtooth wave is outputted to a voltage control oscillator, the oscillation frequency of the voltage control oscillator is constantly varied within a range of fL to fH, and a frequency wherein a piezoelectric vibrating element can be driven can always be ensured, making it possible to drive reliably the piezoelectric vibrating element (piezoelectric actuator).
However, as described in Prior Art 1, when the oscillation frequency is swept, the frequency range in which the piezoelectric vibrating element can be driven is actually part of the frequency range fL to fH, and this drive frequency range varies depending on fluctuations in the surrounding temperature, the load, and the like. Therefore, since the drive signal output from the voltage control oscillator continues even in frequency ranges in which the piezoelectric vibrating element is not driven, unnecessary power consumption occurs.
Further, since the frequency range in which the piezoelectric vibrating element can be driven fluctuates due to fluctuations in the surrounding temperature and the load, the intervals (times) during which the piezoelectric vibrating element is actually driven also fluctuate while the oscillation frequency is swept from fL to fH. Therefore, when the driven object is rotated or moved by the piezoelectric vibrating element, nonuniformities occur in the amount by which the driven object is driven per unit time. Specifically, the drive speed and driving efficiency cannot be improved.
Further, in piezoelectric actuators, individual differences and characteristic differences occur as a result of nonuniformities in manufacturing the piezoelectric element, as well as nonuniformities in the angle of contact between the piezoelectric element and the driven object, the contact pressure, and the like.
Therefore, as described in Prior Art 1, when the oscillation frequency is swept, problems are encountered with the occurrence of nonuniformities in the speed at which the driven object is driven by the piezoelectric actuator, for example, in the rotating speed of the rotor when a rotor is rotatably driven, as a result of individual differences and the like in the piezoelectric actuator.
Problems with the occurrence of nonuniformities in the drive speed are also encountered when the piezoelectric actuator degrades.
In order to eliminate such nonuniformities in the drive speed and to drive the driven object in a stable manner, it is necessary to have a speed adjustment mechanism in which the drive state of the driven object, for example, the rotational frequency over a specific time in a case in which the driven object is a rotor, is determined. It is also necessary that the driving of the piezoelectric actuator is feedback-controlled on the basis of this information, which leads to problems of complicating the control and increasing costs.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a piezoelectric actuator, a drive apparatus for a piezoelectric actuator, an electronic device, a control program for the drive device of a piezoelectric actuator, and a recording medium. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.